function setModelType(f,option_no) {
  var i=0;
  
  // clear selection options	 
  while (i < f.category.length) {
    f.category.options[i] = null;
    i++;
  }

  f.category.options[0] = new Option("Choose Synthesizer Type:","synthesizer.html");

  if (option_no == "coax") {

    f.category.options[1] = new Option("Show All","synthesizer_cx_all.html");
    f.category.options[2] = new Option("Fixed Frequency","synthesizer_cx_fix.html");
    f.category.options[3] = new Option("Tunable Narrow Bandwidth","synthesizer_cx_nar.html");
    f.category.options[4] = new Option("Tunable Medium Bandwidth","synthesizer_con.html");
    f.category.options[5] = new Option("Tunable Wide Bandwidth","synthesizer_con.html");
    f.category.options[6] = new Option("Tunable Very Wide Bandwidth","synthesizer_con.html");
    f.category.options[7] = new Option("Tunable Fast Settling Time","synthesizer_con.html");
    f.category.options[8] = new Option("Dual Frequency","synthesizer_con.html");
  }
  else if (option_no == "sm") {

    f.category.options[1] = new Option("Show All","synthesizer_all.html");
    f.category.options[2] = new Option("Fixed Frequency","synthesizer_fixed.html");
    f.category.options[3] = new Option("Tunable Narrow Bandwidth","synthesizer_nar.html");
    f.category.options[4] = new Option("Tunable Medium Bandwidth","synthesizer_med.html");
    f.category.options[5] = new Option("Tunable Wide Bandwidth","synthesizer_wide.html");
    f.category.options[6] = new Option("Tunable Very Wide Bandwidth","synthesizer_vwide.html");
    f.category.options[7] = new Option("Tunable Fast Settling Time","synthesizer_fset.html");
    f.category.options[8] = new Option("Dual Frequency","synthesizer_dset.html");
  }

}